Rapid Trio Exome Sequencing for Autosomal Recessive Renal Tubular Dysgenesis in Recurrent Oligohydramnios

Oligohydramnios is not a rare prenatal finding. However, recurrent oligohydramnios is uncommon, and genetic etiology should be taken into consideration. We present two families with recurrent fetal oligohydramnios that did not respond to amnioinfusion. Rapid trio-whole-exome sequencing (WES) revealed mutations in the AGT gene in both families within 1 week. The first family had a compound heterozygous mutation with c.856 + 1G > T and c.857-619_1269 + 243delinsTTGCCTTGC changes. The second family had homozygous c.857-619_1269 + 243delinsTTGCCTTGC mutations. AGT gene mutation may lead to autosomal recessive renal tubular dysgenesis, a rare and lethal disorder that can result in early neonatal death. Both the alleles identified are known alleles associated with pathogenicity. Our findings suggest that trio-WES analysis may help rapidly identify causative etiologies that can inform prompt counseling and decision-making prenatally.

Renal Tubular Dysgenesis Associated with Compound Heterozygous ACE Mutations

Inherited renal tubular dysgenesis(RTD), a rare, autosomal recessive disorder is caused by mutations in the genes encoding components of the renin-angiotensin pathway: angiotensinogen(AGT), renin (REN), angiotensin-converting enzyme(ACE), and angiotensin ?? receptor type 1(AGTR1). It characterized by the absence or poor development of renal tubules, and associated with oligohydramnios, Potter sequence and neonatal death due to renal or respiratory failure. We report a family with two mutations in the coding region of the ACE gene: a nonsense mutation in exon4 (c.538C>T) and a frameshift deletion at nucleotide 3073 and nucleotide 3074 in exon20(c.3073_3074delTC). The mutations were in the compound heterozygous state causing disease, because each parent had their own mutation.

Effect of Hydrocortisone on Angiotensinogen (AGT) Mutation–Causing Autosomal Recessive Renal Tubular Dysgenesis

We has identified a founder homozygous E3_E4 del: 2870 bp deletion + 9 bp insertion in AGT gene encoding angiotensinogen responsible for autosomal recessive renal tubular dysgenesis (ARRTD) with nearly-fatal outcome. High-dose hydrocortisone therapy successfully rescued one patient with an increased serum Angiotensinogen (AGT), Ang I, and Ang II levels. The pathogenesis of ARRTD caused by this AGT mutation and the potential therapeutic effect of hydrocortisone were examined by in vitro functional studies. The expression of this truncated AGT protein was relatively low with a dose-dependent manner. This truncated mutation diminished the interaction between mutant AGT and renin. The truncated AGT also altered the glucocorticoid receptor (GR)-dependent transactivation, indicating that AGT may affect the development of proximal convoluted tubule by alteration of glucocorticoid-dependent transactivation. In hepatocytes, hydrocortisone increased the AGT level by accentuating the stability of mutant AGT and increasing its binding with renin. Therefore, hydrocortisone may exert the therapeutic effect through the enhanced stability and interaction with renin of truncated AGT in patients carrying this AGT mutation.

Anhydramnios, but prenatally normal kidneys: renal tubular dysgenesis – patient with mutations in the renin-angiotensin system gene AGTR1

BackgroundPrenatally detected oligo- or even anhydramnios may – beside other reasons – be indicative for a diminished or absent urine production. The resulting clinical picture is a “Potter sequence” with arthrogrypotic joint contractions, a flat face and most importantly pulmonary hypoplasia. In severe cases this pulmonary hypoplasia can be life-limiting irrespective of the underlying lesion.Case presentationOur patient initially presented with anhydramnios and normal kidneys at external ultrasonography after 31 weeks of pregnancy. Following spontaneous birth after 37 weeks of gestation, the baby boy was born with all the clinical signs of a “Potter-sequence” along with a severe pulmonary hypoplasia leading to insufficient oxygenation and ventilation. Despite all measures taken, the child died after 8 h of life. Beside life-limiting pulmonary hypoplasia postmortem examination again confirmed macroscopically normal kidneys, but microscopy showed compact and variable sized glomeruli, numerically reduced and immature tubules, a structurally altered renal vascular bed and an expanded medullar interstitium. Immunohistochemical studies revealed the absence of proximal convoluted tubules, shortened proximal straight tubules beside an immaturity and dysmorphogenesis of the other segments of the nephron, and thus proved renal tubular dysgenesis (RTD) as the underlying disease. A homozygous mutation c.377G>C (p.Arg126Pro) in exon 2 of the AGTR1 gene was found, leading to the exchange of a highly conserved arginine to proline. This mutation has not been reported in public databases so far. As expected, both consanguineous parents were heterozygous for this mutation.ConclusionRTD has to be considered in an anuric fetus with apparently normal renal sonography in order to allow adequate prenatal counseling and – if indicated – palliative postnatal care.